Microstructural Investigation of Soil Suction and Hysteresis

In partially saturated cohesive soils, very large values of suction have been measured — in the order of more than 100 times the atmospheric pressure. A clear understanding of the precise nature of the microscopic mechanisms that lead to such large suction values is still lacking. Furthermore, the soil-water characteristic curve (SWCC) is found to be different for drying and wetting, exhibiting a form of hysteresis. The causes of hysteresis are still poorly understood. In the present study, molecular dynamics (MD) is used to develop an understanding of the capillary menisci that forms between two clay particles. Based on the results of MD analyses and existing macroscopic capillary theories, a model is proposed for the prediction of SWCC and the associated hysteresis. Numerical specimens prepared by the discrete element method (DEM) are used in the study. The input for the model is derived from the results of MD and DEM. It is shown that the theoretical results from the model are consistent with existing experimental observations.